The present invention relates to a line output transformer for a television set, including a number of windings, for connecting the line output stage to the horizontal deflection coil(s) and for supplying voltage to other auxiliary circuits, the transformer having at least a ferromagnetic core and an insulating support for the said windings, the said support being designed to accommodate a number of metal terminals for connecting the said windings to the remaining circuitry of the set.
The current design practice in modern television sets is to use the line output stage as a voltage source for supplying or controlling many if not all the circuits of the set. A consequence of this practice is that the line output transformer (or extra-high tension (EHT) transformer as it is also called, as it also generates the acceleration voltage for the C.R.T. anode) has a number of different windings, some isolated and others connected in series.
The current practice is to wind the windings onto two separate supports to form two coils of which one, termed the primary coil, contains all the windings with the exception of the EHT winding and the other is called the EHT coil, or tertiary coil, as the primary coil contains the primary winding connected to the line output stage and various secondary windings.
The two coils, at least in Europe, are usually arranged parallel to one another on two opposite parallel branches of the ferromagnetic core.
The primary coil, which has many output terminals (usually more than ten), is wound in one of the following two ways, namely:
1. Ten or fifteen coils at a time are wound on a multispindle winding machine and sheets of plastics (polyester or polycarbonate) material are inserted between one layer and the next. The multiple windings are then cut to obtain the individual windings of the primary coil; and
2. A SINGLE PRIMARY COIL IS WOUND AT A TIME.
The first method is quick and there are programmable, semi-automatic machines which stop automatically after each winding or part winding has been wound to insert the insulating material between one layer and the next. The start and end of each winding must be held in place by the operator with adhesive tape.
Once the primary coils are wound and separated from one another:
THE START AND END OF EACH WINDING OF EACH COIL MUST BE PULLED OUT USING A CROCHET HOOK WHICH IS A DELICATE, TEDIOUS OPERATION, AND
THE PRIMARY COIL MUST BE MOUNTED ON THE COIL SUPPORT CARRYING THE TERMINALS AND THE ENDS OF THE WINDING MUST BE WRAPPED AROUND AND SOLDERED TO THE TERMINALS.
In the second method, each coil is wound directly on the support but the method is much slower. At each stop, the operator must tape down the wire and wind the ends around the appropriate terminals to which they are subsequently soldered.
It is more difficult, using the second method, to insert the insulating sheets between layers automatically.
It is also known (see for instance U.S. Pat. Nos. 2,982,888 and 3,644,986) to wind transformers and more particularly television transformers on grooved coil supports so that the individual windings are insulated one from the other; but with such a method there is a problem as to how to insulate inside a groove the starting end of a winding from subsequent turns and how to make in a simple and inexpensive way the connections of the ends of the windings and the remainder of the circuit.